The present invention is directed to a thin-film solar cell arrangement comprising at least one first solar cell and one second solar cell of the pin-type or nip-type that are arranged relative to one another as a tandem cell. Each cell comprises a p-layer, an i-layer, an n-layer, and electrical contacts. The thin-film cell is suitable for module structure with series interconnection
W. Heywang, "Amorphe und polykristalline Halbleiter", Springer Verlag, Berlin, Heidelberg, New York, Tokyo 1984, pages 58 through 64, for example, discloses thin-film solar cells that contain what is referred to as a pin junction. An undoped, i.e., i-layer, is provided with a p-layer on one side and with an n-layer on an opposite side. The i-layer can be constructed based on amorphous silicon.
In order to be efficient, a solar cell of amorphous silicon must have a uniform and optimally high electrical field through the entire absorption zone. In this regard, it should be noted that the higher the electrical field strength in the i-layer, the less the solar cell ages. A higher field strength is achieved, for example, by utilizing a thinner i-layer. Only part of the incident light, however, is thereby still absorbed.
It is known to stack a plurality of series-interconnected pin-cells on top of one another; see, for example, W. Heywang, "Amorphe und polykristalline Halbleiter", Springer Verlag, Berlin, Heidelberg, New York, Tokyo 1984, page 64. This results in an increase in the absorption of the light. The no-load voltage of the arrangement is increased due to the series interconnection.
When two solar cells are stacked on top of one another, this is usually referred to as a tandem cell. Such a tandem cell is disclosed in, for example, J. Yang, International Conf. on Stability of a-Si Alloy Materials and Devices, 28-30 Jan. 87, Palo Alto, Calif., pages 295-303.
In order to better exploit the spectrum of incident light, two solar cells are combined in a tandem cell that absorb light in different wavelength ranges; see, for example, J. Yang, Intern. Conf. on Stability of a-Si Alloy Mat. and Devices, 28-30 Jan. 87, Palo Alto, Calif., pages 295-303. The differing wavelength sensitivity of solar cells is achieved by utilizing different additives to the amorphous silicon of the i-layer, such as, for example, carbon, germanium, or fluorine.
One of the difficulties that arises in creating tandem cells is matching the electrical values of the two cells that are stacked on top of one another and connected in series. In the series circuit, the overall voltage of the tandem cell of the arrangement is the sum of the individual voltages. The current in both individual solar cells in the tandem cell must be identical if losses are to be avoided. Matching the electrical values is achieved, for example, by matching the thicknesses of the two i-layers.
Another method (see, for example, C. Eberspacher et al, 18th IEEE, Las Vegas 1985, pages 1031-1035) is to produce the two solar cells so that they are completely insulated from each other, for example, on different sides of one substrate or on two substrates. Each solar cell can then be provided with two contacts that can be independently wired. But, locating the solar cells on the different sides of the substrate is an involved process and requires great care. The interconnection of the solar cells is extremely labor-intensive due to the many individual contacts.